package demo3;

public class Computer {
    public void powerOn(){

        System.out.println("打开电脑");
    }
    public void powerOff(){
        System.out.println("关闭电脑");
    }
    public void useDevice(USB usb){
        usb.openDevice(); //向上转型
       if(usb instanceof Mouse){
            Mouse mouse = (Mouse)usb;
            mouse.click();
       }else if (usb instanceof Keyboard){
            Keyboard keyboard = (Keyboard) usb;
            keyboard.input();
       }
        usb.closeDevice();//向上转型
    }
}
